The present invention relates to improvements in optical disk drives and scanning methods.
Optical disk drives are devices that can read, and possibly also write data on, and erase data from, optical disks. The data may be analog or digital, and may contain computer data, video, audio, or other information. To be able to read data, an optical disk drive needs to focus laser light to a spot about 1 xcexcm or less in diameter on a recording surface area of the disk, then collect the light reflected from that spot. It also needs to reach any point on the recording area of the disk quickly. To record on rewritable optical disk media, the drive must additionally be capable of delivering sufficiently high laser power into this spot, and must have means to modulate the intensity of the light.
The conventional optical disk drive has a head, typically containing one or more semiconductor lasers, lenses and other optical devices, optical detectors and electromechanical focus and tracking actuators. To reach a particular location on the disk, the head moves essentially along a radius of the disk, while the disk is rotating. Since the head is complex and contains many optical and mechanical parts, it is heavy, resulting in slow acceleration. Therefore, the time it needs to reach a particular destination, the seek time, is relatively long. This long seek time is even more disturbing when compared with that of hard disk drives in which ultra lightweight magnetic heads are employed. It is well known that the overall performance of a disk drive is strongly affected by the seek time.
Several attempts to overcome or circumvent these limitations of conventional optical disk drive technology have been described. Two of these, both using one or more laser beam scanners with an array of focusing elements, will be discussed below.
While many attempts to improve optical disk drives have been made and described in publications, they are primarily intended to improve the transfer rate of data between the optical disk media and the electronic signal processing channel, usually by applying parallelism. Transfer rate is the number of bytes per second that can be read or written after the correct physical disk location has been accessed. A well-known approach to increasing transfer rate without increasing the rotational speed of the disk is parallel access. However, the known implementations of this approach do not support decrease of seek time. In practice, since they all add complexity and weight to the moving head, they should actually increase the seek time. In addition, they are applicable only to readout and are not intended to support multiple track writing.
However, although increase in transfer rate would be desirable, it is presently believed that access time is far more significantxe2x80x94for most computer based applications the time spent getting to the correct location on the disk far exceeds the raw transfer time. Access time is the sum of seek time, which is the time it takes the head to reach a specific track, and latency, which is the time needed for the disk to rotate until the right part of the track (sector) is next to the head. Access time is the combination of seek time and latencyxe2x80x94the total time from initiation of commands till actual read/write operation can start. It has been proposed to decrease the seek time in optical disk drives by decreasing the weight and size of the moving head, essentially, for example, by splitting the head into a stationary part and a lighter moving part or by adopting substrate-mode optics, or planar optics, in the internal construction of the moving head. Neither technique can approach the order of magnitude of the weight of heads already deployed in non-optical magnetic computer disk drives, or hard disk drives (HDDs).
The different characteristic of light, as opposed to electrons, makes miniaturization of the optical system of a moving-head optical disk drive to the order of magnitude of the size already employed in HDD heads inherently extremely difficult.
Glaser, U.S. Reissue Patent No. Re 36,393, entitled Two-dimensional random-access scanning for optical disks, reissued on Nov. 16, 1999, the disclosure of which is incorporated herein by reference, discloses an arrangement, as shown in FIG. 1 (taken from that patent), that uses two-dimensional (2D) scanning and a 2D array of light focusing devices, such as a 2D lenslet array. In FIG. 1, light that is generated by a laser 2 passes through beam shaping optics 5 and is then redirected by a two-dimensional optical scanner. The optical scanner is composed of two moving mirrors 7 and 8 and two electromechanical actuators, M1 and M2 toward a two dimensional array of focusing elements 1, depicted as a lenslet array. Each focusing element in the array addresses a range of tracks on the recorded, or recording surface area 3 of the disk. The specific track selected depends on the precise angle at which the laser light reaches that lenslet. For readout, light focused on the track is reflected back through the same lenslet, acting as a xe2x80x98cat-eyexe2x80x99 retro-reflector to send light back toward its source. This retro-reflected light is intercepted by a beam splitter 11 towards a stationary detector head 12. The detector head, with its associated electronics, derives signals for the data on the disk, as well as for servo controls such as tracking and focus.
Damen et al, U.S. Pat. No. 4,550,249, entitled Optical disk read/write apparatus, issued on Oct. 29, 1985, the disclosure of which is incorporated herein by reference, describes a different type of optical and mechanical configuration for an optical disk drive scanning system.
The basic embodiment of this configuration has two lenslet arrays (10, 11 and 12 in FIGS. 2A, 11, 12, 13, 21, 22, and 23 in FIG. 2B, FIGS. 2A and 2B being taken from the Damen at al patent), one above the other, with a set of semi-reflecting, or slotted, mirrors between them (41, 42 and 43 in FIG. 2B). A laser beam 50 from a laser 16 is directed by a series of mirrors 18, 19 and 30 towards the gap between the two arrays. This laser beam 50 is split by a first semi-reflecting mirror 41 and the reflected beam is directed through, and focused by, a lenslet 11 toward a disk data storage and/or recording surface 14. The beam is then reflected by the same disk surface, passes through lenslets 11 and 21 and semi-reflecting mirror 41 and is imaged onto a detector array 15. Laser beam light that passes through mirror 41 is then split by semi-reflecting mirror 42, where it is focused on another location on the disk recording surface 14 and imaged onto the detector array 15, and so on. Sufficient optical power must be provided to allow this multiple parallel access. The beam steering system of moving mirrors 18 and 19 is one-dimensional in the sense that it can move the laser beam only in a single plane.
A drawback of this prior art system is that writing is essentially impractical. Since all of the illuminated tracks get the same signal, they would all be written by the same data, resulting in multiple copies and a vastly smaller effective data capacity. Laser power is distributed over many tracks, so a very powerful laser is needed to obtain sufficient writing energy. Wrong tracks will be accessed. The same patent describes an alternative configuration with slit mirrors instead of beam splitter, but a simple calculation shows that these slit mirrors will cause the focused spot to become larger, intolerably decreasing the data capacity of the disk. While that system allows parallel access, the tracks that are accessed together are not adjacent ones. As a result, tracks are read in the wrong order, at least for removable disks that are formatted for conventional drives.
This scheme seems to provide both fast access and parallel (high data rate) readout. However, since the accessed tracks are far from each other, focusing errors, due to surface irregularities etc., will probably be uncorrelated, so that central focus correction is unlikely to work.
It is an object of the present invention to provide substantial improvements to optical disk drives and scanning methods, enhancing their capabilities while lowering the cost of manufacturing such optical disk drives.
This invention achieves such improvements, in part, by moving light beams instead of optical heads.
Objects according to the invention are achieved by the provision of apparatus for scanning an optical disk that is mounted for rotation with a data surface of the disk disposed in a scanning plane, the disk data surface having light reflecting areas, the apparatus comprising:
a light source for producing a relatively narrow beam of light;
a scanning assembly for directing the beam toward the scanning plane and causing the beam to traverse the scanning plane;
a focusing lens unit disposed in the path of the beam to focus the beam at the scanning plane; and
a light beam deflecting element disposed in the beam path between the scanning assembly and the focusing lens unit to deflect the beam toward a direction perpendicular or near perpendicular to the scanning plane.
When reference is made herein to a data surface, or a disk surface carrying data, it is to be understood that the data surface in optical disks is sometimes an internal surface where the disk is made of two cemented thinner pieces, as in a DVD, or a surface at the side opposite to the laser source, as in a CD.
Objects according to the invention are further achieved by apparatus for scanning an optical disk that is mounted for rotation with a surface of the disk disposed in a scanning plane, the disk disposed in a scanning plane, the disk surface having a light reflecting areas arranged in a plurality of mutually parallel, or near parallel, tracks, the apparatus comprising;
a light source for providing a relatively narrow beam of light and directing the beam along a selected path;
a focusing unit comprising a group of individual light focusing elements, possibly, lenses spaced apart parallel to the scanning plane each having an optical axis that is essentially perpendicular to the scanning plane and each being associated with a respective track; and
light directing means disposed in line with the path at a location for directing light from the light source substantially entirely to a respective one of the individual lenses.
To aid understanding of the present disclosure, specific examples of key components are often used instead of the more general terms. It is to be understood that this terminology should not be interpreted as to exclude the use of substitute or equivalent devices and/or sub-systems. In all cases, any device or sub-system mentioned in the text, and/or shown in the drawing specifically refers to any and all possible substitute or equivalent devices and/or sub-systems, which are all covered by the invention, its embodiments, and examples. As specific cases, without excluding others, note the following terms:
Lensesxe2x80x94are generalized to any optical imaging, light-focusing, and/or light diverging devices, including, but not limited to,
simple refractive lenses of all suitable kinds, possibly with an aspherical surface or surfaces,
reflective optical elements that can perform the required function
systems comprising one or more reflective, and one or more refractive, optical elements, or an element or elements that both refract and reflect light,
diffractive optical elements,
holographic optical elements,
elements combining refractive, and/or reflective, and/or diffractive, and/or holographic, surfaces,
and/or
compound optical systems (comprising several simple lenses and/or other optical elements including all or any of those described above, with suitable mechanical mount, if needed),
Lenslet arraysxe2x80x94may be substituted by arrays of small xe2x80x9clensesxe2x80x9d (=lenslets) as defined just above. It is noted that not all xe2x80x9clensesxe2x80x9d in a single array must be identical, and that the centers of the xe2x80x9clensesxe2x80x9d may not necessarily, in fact are likely not to be, arranged in a Cartesian or other periodic array. The term xe2x80x9clensletxe2x80x9d is thus used here to refer to a small lens in the generalized sense defined above, typically of aperture not larger than 10 millimeters.
Scannersxe2x80x94are any devices that are used to change the direction of a light beam, as directed by signals that are generated by an electronic system. In addition to the mechanical actuator/moving mirror assemblies depicted in the drawings herein, some other possible types are:
MEMS (Mechanical Electronic Micro Systems) or MEOMS (Mechanical Electro-Optical Micro Systems) scanners, including those disclosed in: M. Edward Motamedi, Angus P. Andrews, William J. Gunning and Moshen Khosh-nevisan, xe2x80x9cMiniaturized micro-optical scanners,xe2x80x9d Optical Engineering 33(11), 3616-3623 (1994); xe2x80x9cBeam deflectors will be smaller and faster,xe2x80x9d Opto and Laser Europe (issue 68), 20{21)(November 1999); and xe2x80x9cSandia micromirrors may be part of Next Generation Space Telescope,xe2x80x9d Internet URL www.sandia.gov/media/NewsRel/NR1999/space.htm (November 1999).
Electro-optical beam steering devices
Acoustic-optical scanners
other types of opto-mechanical scanning devices, such as, for example, scanners based on
moving or rotating prisms,
systems containing lenses that move essentially perpendicularly to their optical axis
moving diffraction gratings, etc.
Prismsxe2x80x94may be substituted by suitable gratings, possibly holographic or diffractive.
It is also noted that optical systems can be xe2x80x9cfoldedxe2x80x9d to decrease their volume and/or footprint. Such folded variants of the systems covered by this invention are also explicitly included.
The terms xe2x80x98lensxe2x80x99, xe2x80x98lensletxe2x80x99, xe2x80x98lensesxe2x80x99 and xe2x80x98lensletsxe2x80x99 are used throughout the following description, and drawings of lenses and lenslets appear in the figures as examples of general light focusing element or elements. Whenever these terms are used, they are intended to mean any optical device for focusing light, including, but not limited to, refractive lenses and lenslets, diffractive optical elements, Fresnel lenses and lenses and suitable holographic optics. Reference is made to Selected Papers on Holographic and Diffractive Lenses and Mirrors, T. W. Stone and B. J. Thompson, editors, (SPIE Optical Engineering Press, Bellingham Wash., 1991) and the bibliographies therein.
Conventional optical disk drives contain heads that move in order to access a specific track on the disk. These moving heads typically contain a laser (or sometimes, several lasers), at least one lens, other optical elements, detectors, and actuators that enable focus and track following. Some split head designs keep some of these elements further away from the moving head, in order to reduce moving mass and thus allow shorter seek times, seek time being the time needed to get to a specific track. Embodiments of the invention achieve, or approach, the following results:
move everything except the last focusing lens away from the disk surface; and
in some embodiments, replace a single moving lens by an array of stationary lenses, or other light focusing elements, so that there would be no need to have any moving head next to the disk surface;
The invention can also serve to increase the transfer rate of data and to decrease the latency, which is the time needed to wait until, through the rotation of the disk, the proper sector of the track gets next to the lens.
The invention offers one or more of the following improvements over systems of the type disclosed in the above-cited Glaser patent: accurate beam positioning can be achieved with relatively inexpensive lenses; less expensive, and potentially more compact, scanners can be used to obtain improved performance; the transfer rate of data, represented by the number of bytes per second read or written once the correct track and sector on the disk have been accessed, can be increased; and the latency, which is the wait time needed while the disk rotates to the correct position to start reading or writing, can be reduced without increasing the rotation speed of the disk.